Forest Structures, Composition, and Distribution on a Pacific Island, with Reference to Ecological Release and Speciation!

Home , Bonin Islands, Pandanus boninensis, Rhaphiolepis indica, Sambucus javanica, Schima, Stachyurus praecox

YOSHIKAZU SHIMIZU2 AND HIDEO TABATA 3

ABSTRACT: Native forest and scrub of Chichijima, the largest island in the Bonins, were classified into five types based on structural features: Elaeocarpus Ardisia mesic forest, 13-16 m high, dominated by Elaeocarpus photiniaefolius and Ardisia sieboldii; Pinus-Schima mesic forest, 12-16 m high, consisting of Schima mertensiana and an introduced pine , Pinus lutchuensis; Rhaphiolepis Livistonia dry forest, 2-6 m high, mainly occupied by Rhaphiolepis indica v. integerrima; Distylium-Schima dry forest, 3-8 m high, dominated by Distylium lepidotum and Schima mertensiana; and Distylium-Pouteria dry scrub, 0.3 1.5 m high, mainly composed of Distylium lepidotum. A vegetation map based on this classification was developed. Species composition and structural features of each type were analyzed in terms of habitat condition and mechanisms of regeneration. A group of species such as Pouteria obovata, Syzgygium buxifo lium, Hibiscus glaber, Rhaphiolepis indica v. integerrima, and Pandanus boninen sis, all with different growth forms from large trees to stunted shrubs, was subdominant in all vegetation types. Schima mertensiana , an endemic pioneer tree, occurred in both secondary forests and climax forests as a dominant canopy species and may be an indication of "ecological release," a characteristic of oceanic islands with poor floras and little competitive pressure. Some taxonomic groups (Callicarpa, Symplocos, Pittosporum, etc.) have speciated in the under story of Distylium-Schima dry forest and Distylium-Pouteria dry scrub. Specia tion seems to have occurred exclusively where there are comparatively small numbers of component species, historically stable habitats, some opportunity for regeneration without large-scale disturbance, and the occasional occurrence ofcanopy gaps.

THE BIOTA OF OCEANIC ISLANDS is derived from Mueller-Dombois 1981), Galapagos Islands ancestors that arrived by chance across an (Wiggins and Porter 1971, Eliasson 1984, open sea and became established. The fauna Hamann 1984), and Ponape, in the Caroline and flora of those islands have many char Islands (Nakamura 1985). Moreover, the acteristics that distinguish them from those of structure and quantitative composition of continents (see Carlquist 1974). There are plant communities have been analyzed with- many oceanic islands in the Pacific Ocean, but out consideration of insular phenomena such there is relatively little information about as ecological release and speciation. their vegetation except for the well-known The Bonin Islands (Ogasawara-shoto in Hawaiian Islands (Rock 1913, Fosberg 1961, Japanese), located about 1000 km south of Tokyo in the northwestern Pacific Ocean (Figure 1), are Japan's only typical oceanic I Manuscript accepted 10 April 1990. islands. They consist of about 30 islets occur 2 Department of Natural Sciences, The Komazawa ring in four main groups located linearly University, Koma zawa 1-23-1, Setagaya-ku, Tokyo 154, Japan. north to south: Mukojima, Chichijima, Haha 3 Laboratory for Plant Ecological Studies, Faculty of jima, and Iwojima. Even the largest island, Science, Kyoto University, Sakyo-ku , Kyoto 606, Japan. Chichijima, is comparatively small, 2395 ha in 28 Forest Structure on a Pacific Island-SHIMIZU AND TABATA 29

Chichi jima I.

20 -/--f------,~----t----';--___j_

FIGURE 1. Location ofthe Bonin Islands and a geographical map ofChichijim a Island. Thin lines on the map show the IOO-m contour. Triangles mark principal mountains. area and 319 m highest elevation . The islands vegetation map for Chichijima. Okutomi et al. are volcanic, dating back to the Tertiary (1985) published vegetation maps for the (Mukojima, Chichijima, and Hahajima) or main islands of the Bonins. Ohba and Suga Quaternary (Iwojima) (Kuroda et al. 1981). wara (1977) and Okutomi et al. (1985) made The climate issubtropical. It rains almost year a detailed classification based on the Braun round, but soil water deficiency occurs in mid Blaunquet method of analysis. There are also summer in areas with shallow soil (Figure 2). ecological studies of the vegetation ofChichi Ninety-nine families, 256 genera, and 369 jima and Hahajima by Numata and Ohsawa species of vascular plants are found in the (1970) and Ohga et al. (1977). None of these Bonins. The proportion of endemism is 42.5% is sufficient, however, to describe a situation for all flowering plants and 74.7% for in which forest and scrub represent a stage on arboreal species alone (Kobayashi 1978). The which a drama of evolution is played. flora of the Bonins is related to that of sub In this paper we classify the native forest tropical Southeast Asia, Formosa, and the and scrub of Chichijima with emphasis on Ryukyu Islands (Hosokawa 1934, Tuyama structural characteristics and show some 1970, Yamazaki 1981). However, some gen unique features. We also attempt to relate era, such as Quercus and Castanopsis, which vegetation structure and composition to are the dominant species in the Ryukyu Is the phenomena of ecological release and lands, are absent in the Bonins (Shimizu, speciation. . 1984a). Nomenclature follows Yamazaki (1970) Toyoda (1975) classified the vegetation except for Rhaphiolepis indica v. integerrima based on dominant species and proposed a and Cinnamomum insularimontanum. 30 PACIFIC SCIENCE, Volume 45, January 1991 1609mm (mm) 300 200 100 80 60 40 10 20

J FMAMJ J ASONDJ

FIGURE 2. Climate diagram of Chichijima Island based on monthly mean temperatures and precipitation recorded from 1907to 1939.

METHODS quadrats, randomly placed in each plot and covering at least 10% of the plot area . The native forest and scrub of Chichijima Profile diagrams were drafted, light inten was typified mainly by structural character sity was measured at ground level, and leaf istics derived from field observation. Aerial size (length and width) of all component photographs (scale 1 : 12,500)and ground ob species was measured with collected samples servations were combined to produce a vege in the typical forest and scrub ofeach type. tation map. Fifty plots, including each type of forest and scrub, were sampled in 1977 and 1979. RESULTS The forest vegetation was stratified into four height layers: Tl, the canopy tree layer; T2, Typification the low-stature tree layer; S, the shrub layer; and H , the herbaceous plant layer including The native forest and scrub on Chichijima seedlings of canopy species. Fewer layers were were classified into three main groups on the recognized in scrub. An emergent layer con basis of average height of canopy trees: mesic sisting exclusively of mature Pinus lutchuensis forest with tall trees, 10-15 m high; dry forest trees was designated the E layer. with low-stature trees, 2-10 m high; and dry All vascular plant species were enumerated. scrub with shrubs less than 2 m high. These Tree diameters (~3 em) were measured at groups were subdivided into fivetypes (Figure 1.2 m above ground except for shrubs less 3) in terms of structural features other than than 1.5 m high, for which stem girth was tree height (e.g., presence of an E layer and measured at ground level. Seedlings in the development of undergrowth shrubs). Types H layer and saplings ( < 3 em) were counted. were named by dominant or subdominant Herbs and vines were tallied in 1 m x 1 m species. A. E-A rn.f, C. R-L d.f.

O. 0-5 d.f.

B. p-s m.f.

E. O-P d.s.

1m 3mx 20m

F IGURE 3. Profile diagrams of the five vegetatio n types. The size of sample strips is shown at bottom right of each. Keys to abbreviations: Ar, Ardisia sieboldii; Bl, Boninia glabra; Cy, Cyathea mertensiana; 01, Distylium lepidotum ; El, Elaeocarpus photiniaef olius; Hi, Hibiscus glaber; Ip , !lex percoriacea; Li, Ligustrum micrantum; Liv, Livistonia chinensis; Me, M elia azedarach; Pa, Pandanus boninensis; Pi, Pinus lutchuensis; Pis, Pisonia umbellifera; Po, Pouteria obovata ; Rh, Rhaphiolepis indica v. integerrima; Sb, Syzygium buxifolium; Sk, Symplocos kawakamii; Sm, Schima mertensiana ; Sp, Symplocos pergracilis; St, Sta chyurus praecox v. matsuzakii. 32 PACIFIC SCIENCE, Volume 45, Jan uary 1991

Elaeocarpus-Ardisia mesic forest (E-A m.f.) undergrowth shrubs occur in this kind of for is the tallest forest of all. Canopy trees attain est (Figure 3D). 15 m in height. Elaeocarpus photiniaefolius is Distylium-Pouteria dry scrub (D-P d.s.), of abundant in the canopy layer; lower layers are O.3-1.5-m-high vegetation, is also dominated dominated by Ardisia sieboldii (Figure 3A) . by Distylium lepidotum. Almost all species in Pinus-Schima mesic forest (P-S m.f.), 12 this scrub have stunted growth forms (Figure 15 m high, is dominated by an introduced 3E). pine, Pinus lutchuensis, and an indigenous Figure 4 shows the similarity relationships pioneer tree, Schima mertensiana . The crowns of the sample plots based on the Bray-Curtis of the pine trees reach far above those of the (1957) ordination method. The index of simi other species, forming an emergent layer larity is IS = 200cj(a + b), in which a and b (Figure 3B) represent the total number of species in Plots Rhaphio lepis-Livistonia dry forest (R-L A and B, and c is the number of species com d.f.), 2-6 m high, is dominated by Rhaphio mon to both plots. The ordination, based on lepis indica v. integerrima (Figure 3C). There the composition of woody species, indicates are few shrub species in the S layer. that the plots of each vegetation type, except Distylium-Schima dry forest (D-S d.f.), 3 those of the Pinus-Schima mesic forest, are 8 m high, is mainly composed of Distylium distinctively grouped. Pinus-Schima mesic lepidotum and Schima mertensiana. Many forest is a secondary forest (Shimizu 1983),

oI----r------r-----~..;::",.",,~ ~~--__r_--___r-----r--__,- 10 20 30 [,0 50 60 70 80 A x is 1

FIGURE 4. Ordination of 50 sample plots by the Bray-Curtis (1957) method based on similarity of composition of woody species. Forest Structure on a Pacific Island-SHIMIZU AND TABATA 33 thus the plots of this type are scattered in the layers, the forest is relatively dark (Table 2). ordination (Figure 4) because of varied Few understory shrub species indigenous to species composition, which is affected by sur Elaeocarpus-Ardisia mesic forest are found on rounding climax forests. Typification by Chichijima (Table 3), and seedling density of structural features also seems to be reasonable woody and herbaceous species is low in the from the standpoint of species composition. H layer (Table 1). On Hahajima, the second The variation on axis 1 in Figure 4 shows a largest island , where this type of forest has gradient from mesic forest to dry scrub. Field been preserved in better condi tion, some small observation of a cross section along a road undergrowth trees (Claoxylon centinarium, showed that tree height is roughly propor Ficus iidaiana) , herbaceous plants (Piper tional to soil depth. Thus the gradient may be postelsianum, Corymborchis subdensa, Good related to soil depth and moisture conditions. yera boninensis, Bolbitis boninensis), and epi The variation on axis 2, which seems to sepa phytes (Cirrhopetalum boninense, Peperomia rate the two types ofdry forest , is not attribut boninsimensis, Asplenium nidus) are found . able to anyone environmental variable. The Thus, the Elaeocarpus-Ardisia mesic forest on relation between vegetation and edaphic con Chichijima may have had a richer flora of ditions needs further study. understory shrubs, herbaceous plants, and epiphytes before destruction of the forest by man . Structure and Composition The Elaeocarpus-Ardisia mesic forest was seriously damaged by the exceptionally severe Table I shows the average density of indi viduals for all woody species in each vegeta typhoon that hit the Bonins on 6-7 November tion type. 1983 (Shimizu 1984b). Regeneration of this forest following large-scale canopy gap for Elaeocarpus-Ardisia MESIC FOREST. The mation by typhoons is being investigated Elaeocarpus-Ardisia mesic forest consists of (Shimizu, in preparation). four layers (Figure 5A). The TI layer is com posed ofseveral tall trees such as Elaeocarpus Pinus-Schima MESIC FOREST. There are photinaefolius, Pisonia umbellifera, Pouteria four forest layers in the Pinus-Schima mesic obovata, and Sapindus boninensis (Table 1). forest. The top layer, which consists of Pinus Ardisia sieboldii, with suckering ability , over lutchuensis together with Casuarina equiseti whelmingly dominates the lower layers (Table folia in some plots, forms an emergent layer I). Some mature trees of light-demanding (Figure 5B). The T layer is densely occupied species such as Fagara boninensis, Celtis boni by Schima mertensiana and, to some extent, nensis, Melia azedarach, and Schima mer by other native tree species. tensiana are found without any seedlings and Density of stems and individuals is lowest saplings (Table 1). These trees may have in of all the vegetation types (Table 4), and the vaded earlier canopy gaps and survived in the forest is rather dark (Table 3) because of the forest. Most of the canopy trees have large closed canopy of Schima mertensiana. Seedl leaves compared with those ofthe other vege ings of canopy trees are not abundant (Fig tation types (Figure 6). ures 3B, 5B) . No trees, shrubs, or herbs are Stumps of Morus boninensis more than 1 m unique to Pinus-Schima mesic forest (Tables in diameter are sometimes found in the forest. 1, 3) because it is a secondary forest derived M . boninensis was a member of the canopy from cultivated fields abandoned about 1945 species, but almost all trees ofthis species were (Shimizu 1983). selectively cut before 1945 because of their Pinus lutchuensis in this forest has been timber value (Toyoda 1981). Morus australis, attacked by the pine wood nematode since an escaped species, has replaced the endemic 1979. Many mature pine trees in the emergent species. layer are dead, and the physiognomy of the Because ofthe close upper-forest strata and Pinus-Schima mesic forest has been greatly the dominance of Ardisia sieboldii in the lower changed (Shimizu 1986, 1987). TABLE I

MEAN NUMBER OF INDIVIDUALS (ha") OF ALL WOODY SPECIES SURVEYED IN EACH VEGETATION TYPE

Rhaphiolepis Distylium Elaeocarpus-Ardisia Livistonia Distylium-Schima Pouteria Pinus-Schima MESIC FOREST DRY FOREST DRY FOREST DRY SCRUB MESIC FOREST

SPECIES Tl T2 S H T S H T S H T H ETS H

ii 2 - - 48 ---22i-- l,086-- - 75 2 - - -574 --3,4i6-- 554- -- 515 --3~821- - 2,599 - -1~509 - 1 1. Pouteria obovata 127 211 3,920 2. Rhaphiolepis indica v. integerrima i 6 389 1,334 829 2,148 2,645 3,977 631 418 2,161 791 349 : 292 683 2,045 3. Cinnamomum insularimontanum I 3 55 174 203 190 554 458 24 161 238 155 230 I 7 69 442 4. Pandanus boninensis : 3 41 137 67 184 222 36 394 230 339 773 240 I 83 97 157 5. Syzygium buxifolium : 50 40 10 87 75 1,267 290 408 1,177 1,158 642 : 7 220 277 6. Ficus boninsimae I 17 44 9 6 16 74 5 20 I 36 9 7. Ligustrum micrantum : 14 223 520 838 2,281 6,063 237 1,612 4,780 4,305 2,473 1 91 286 1,394 8. Osman thus insularis : 7 84 46 147 192 369 55 143 143 234 38 : 19 50 164 9. Hibiscus glaber L ~ l~~ ~~ }~__ ~~4 ~~ 2 ~~~ __}2~ J 121 63 11 10. (Arc hontophoenix alexandrae) i 6-- 22 -- - 54- - - -3~ I I. Sap indus boninensis :10 86 55 : 12. Pisonia umbellifera I 7 28 10 I 13. (Morus australis) I 6 31 17 I 14. Celtis boninensis : 6 25 94 : 8 7 15. Melia azedarach I 3 17 I 4

16. Fatsia oligocarpela :L 13 ~I 3 3 :14---7----s------21------7--10i----26----i3s -: 17. Elaeocarpus photiniaefolius 165 37 114 18. Livistonia chinensis v. boninensis :10 128 242 276 201 358 106 94 145 191 : 20 9 49 32 19. Machi/us boninensis I 7 76 251 168 7 58 41 342 528 : 5 38 200 190 20. Schima mertensiana : 3 16 98 83 96 392 108 637 I 96 1,133 493 232 21. Fagara boninensis I 3 26 4 3 21 36 4 32 22. Ardisia sieboldii I 856 2,377 688 22 16 18 18 31 20 I 73 236 57 23. Ochrosia nakaiana : 72 101 13 38 138 37 41 12 : 9 2 24. Boninia grisea I 30 30 13 52 19 18 17 I: 9 37 5 25. Drypetes integerrima : 26 4 4 92 19 36 22 8 : 26. Machi/us kobu I 25 14 29 50 41 108 68 92 48 86 47 27. flex mertensii : 16 25 16 27 13 54 44 42 22 18 6 I 25 28. Neolitsea sericea : 14 31 10 45 65 44 29 164 13l 5 45 42 96 95 29. Psychotria homalosperma I II 4 29 2 4 7 30. (Leucaena leucocephala) : 4 18 85 71 137 440 4 17 11 31. Cyathea mertensiana : 3 3 9 32. Tarenna subsessilis* I 54 48 15 15 211 172 16 59 33. Callicarpa subpubescens* : 37 26 10 40 186 32 34. Pittosporum boninense : 6 85 33 9 5 I 2 51 11 20 86 35. Trema orientalis IL 4 57 10 30 _ I 36. (Casuarina equisetifolia) 160 ---- "7 - - - -10-- - 13- - -- -7 --- - 2 -: 24 9 38 7 37. Myrsine maximowiczii 126 4 69 7 4 : 38. Pouteria boninensis I 9 9 7 14 I 3 39. (Rhus secundanea) [ 7 [ ~ ------~ 40. (Psidium cattleianum) i-- - - -20-- --201 5 '- --.J i ---- 1 8---- \0------9--- - 31 41. Clinostigma savoryana ~------~ 42. Ilex matanoana [76- ---34----461 3 5 43. Evodia nishimurae 121 4 50 : 9 44. Geniostoma glabra 116 12 20 I II 13 17 45. Symplocos pergracilis" : 73 12 [ 46. Ca//icarpa glabra" : 43 151 [ 43 39 47. Pittosporum chichisimense" 1 23 125 I 5240 6 82 48. Sta chyurus praecox v. matsuzakii " : 4 7 1 49. Viburnumjaponicum v. boninsimense" [ 2 I [ 4 4 50. Eurya boninensis" L ~ J 51. Wikstroemia pseudoretusa 176---470---297-- - 29--1 4S--I,082- --7 99--- i 5I l 92 52. (Pinus lutchuensis) [66 31 47 3 14 62 278 39 [ 278 46 16 53. flex percoriacea 113 5 9 5 16 19 166 60 [ 7 54. Gardenia boninensis i 3 24 23 31 2 414 20 1 5 55. Osteomeles boninensis" : 11 8 491 24 5 2,526 508 i 56. Hedyotis grayi* I 19 4 IO 417 2471

57. Photinia wrightiana* [L 14 26 I 28 23 496 58~1 23 6

58. Distylium lepidotum ~23 - - -7i7- -1~24 --~968 - -1~8~ 23 287 85 59. Boninia glabra* I 340 52 777 269: 3 14

60. Vaccinium boninense" IL 14 1 5 ~I

61. Dodonaea viscose" II i549----S6[ 7 62. Juniperus taxifolia" 1443 1401 63. Pittosporum parvifolium" I 80 751 64. Symplocos kawakamii* I 41 [ 65. Myrsine okabeana" : 40 [ 66. Ca//icarpa nishimurae" I 28 I I I 67. Hedyotis mexicana" i 801 68. Z anthoxy lum arnottianum" I II I 69. Boehmeria boninensis" L yJ

NOTE: An asterisk denotes shrubby species. Introduced and escaped species are presented in parentheses. Species with similar distribution patterns are enclosed within dashed lines. rn.f. Mean A. E-A height(ml C. R-L d.t. Tl 14 Mean 10 height(m) ~ 5 T T2 18(0) 5 25(1) 5 H r------,--~ 13(0) 40 30 20 10 0 0 ioooo 2 00 5 21(1) Basal area (rrft ha) No of stems (t ha)

H~ 12(1) 40 30 20 10 0 0 10000 20000 BasaI area (m2thal No of stems (tha) D. 0-5 d.t,

B. P-S rn.f. Mean he.l<;; hHm T

E 1 5 H 40 30 20 10 10000 10 - Basal area (m2tha) No of T 17 E. D-P d.s. r- ~ 5 ~I 5 22(2) 30 20 10 20600 Basal area Crrrlhal No of stems (tha) H~ t=I 21(2) 40 30 20 10 0 0 10000 Basal area (rri'tha l No of stems (tha)

FIGURE 5. Basal area and stem density of woody species in the five vegetation types, presented at the average height of each forest layer. The black part denotes the share of intrinsically shrub species (see Table 1). Numerals on the right show the total number of woody species and the number of intrinsically shrub species (in parentheses) in each forest layer. Forest Structure on a Pacific Island-SHIMIZU AND TABATA 37

80 E-A m.f. TABLE 2 RELATIVE LIGHT INTENSITY INTYPICAL PLOTS OF FIVE 60 VEGETATION TYPES (AVERAGE OF 50 SAMPLING SPOTS) 40 VEGETATION TYPE RELATIVE LIGHT INTENSITY (%) 20 E-A m.f. 0.5 ± 0.2 p-s m.f. 3.6 ± 0.8 o'"---.....I.::-.&....&...:::-&--'--:-'- R-L d.f. 7.9 ± 2.9 1 D-S d.f. 11.2 ± 6.3 80 D-P d.s. 15.9± 11.7 P-Sm.f. 60 Rhaphiolepis-Livistonia DRY FOREST. 40 Rhaphiolepis-Livistonia dry forest includes all dry forests that lack Distylium lepidotum as a 20 canopy-forming species. Rhaphiolepis indica v. integerrima, Pouteria obovata, Hibiscus ou=::I'-'-:=.&....&...::::'-'--:-'-- glaber, Syzygium buxifolum, Pandanus bo ninensis, and Ligustrum micrantum are dom 80 inant or subdominant canopy trees that are -o...e also found in Distylium-Schima dry forest. 60 Livistonia chinensis v. boninensis, Boninia -III Q) 40 ...... grisea, Drypetes integerrima, and Pittosporum U boninense characterize Rhaphiolepis-Livistonia Q) 20 dry forest, though they sometimes appear in a. Distylium-Schima dry forest. III o~~.J.-L-:~-:-'-rI 1 2 3 4 Rhaphiolepis indica v. integerrima is usually o predominant in every forest layer in this forest - 80 D-Sd.f. (Table 1). Other species, for example Pouteria L,., obovata, Syzygium buxifolium, Pandanus Q) 60 .0 boninensis, and Livistonia chinensis v. boninen E 40 sis, become dominant in some places instead ::J of Rhaphiolepis indica v. integerrima. Z 20 The canopy is almost closed in the typical U-J'--'-:::..I.....&..:;~-;-'-- forest of this type, and relative light intensity o on the forest floor is intermediate between that in the Elaeocarpus-Ardisia mesic forest 80 D-Pd.s. and the Distylium-Schima dry forest (Table 3). The understory of the forest is exclusively 60 composed ofjuveniles of the canopy trees, and 40 shrub species are absent (Figure 5C). Seedl ings in the H layer are not abundant. 20 Distylium-Schima DRY FOREST. The 0u....,..JL...... J...,,-~~-:-'- Distylium-Schima dry forest is dominated by Distylium lepidotum and other species com mon to the Rhaphiolepis-Livistonia dry forest Leaf size class including R. indica v. integerrima (Table 1). Schima mertensiana and Elaeocarpus photi FIGURE 6. Diagrams of leaf size classes for each vege tation type. Classification of leaf size was based on niaefolius are also abundant, but they are Raunkiaer (1934): I, <0.25 em"; 2, 0.25-2.25 em" ; 3, uncommon in the Rhaphiolepis-Livistonia dry 2.25-20.25 em" ; 4, > 20.25 em" , forest. The occurrence of Geniostoma gla- 38 PACIFIC SCIENCE, Volume 45 , January 1991

TABLE 3

M EAN F REQUENCY (%) OF O CCURRENCES OF ALL H ERBACEOUS PLANTS I NCLUDI NG W OODY VINES ON THE GROUND

Elaeocarpus Rhaph iolepis Distylium Distylium Pinus Ardisia Livistonia Schima Pouteria Schima SPECIES MESIC FOREST DRY FOREST DRY FOREST DRY SCRUB MESIC FOREST

I. Morinda boninensis i l~2 ------Q5 ------~5 ~) - -- --5. 9~) 1 2.3(v) 2. Tracherospermum f oetidum : 6.1(v) 37.0(v) 17.0(v) 55.6(v) : 11.3(v) 3. Oplismenus compositus 9.4 4.5 2.7 0.6 2.1 4. Nephrolepis cordi/alia 8.1 13.7 3.5(e) 0.3 31.2 5. Psychotria boninensis 1.1 7.3(v) 23.6(v) 2.5 28.2(v) 6. Carex oahuensis 6.1(v) 16.6 17.7 43.1 11.2 7. Carex hatt oriana 1.2 31.1 72.3 65.3 27.1 8. Smila x china v. yanagitai 0.6 1.4(v) 12.5(v) 3.8(v) 5.5(v) 9. Gahnia aspera 2.7 15.1 12.7 20.7 3.6 10. Dianella ensifolia 0.5 7.7 0.8 2.5 0.8 I I. Platanthera boninensis 0.5 3.8 1.5 12. Korthalsella japonica ___~ ~2 ~~ J 13. Goodyera boninensis r -3~3- - 1 14. Cyrtomiumfalcatum I 1.1 : 15. Caesalpinia crista I 0.6 I 16. Jasminum hemsleyi 1L... (v)--'1 , ------l 17. Thelypt eris parasitica 1.1 1.4 0.8 6.3 18. Asplenium nidus 1.5 (e) 1.5(e) 19. Micr olepia strigosa 0.2 0.2 1.5 20. Pteris quadriaurita 13.9 0.01 4.0 21. Luisia boniensis' ~ O ~I W 22. Freycinetia boninensis 2.3(v) 6.8(v) O.4 (v) 23. Pleopeltis boninensis 14.5(v) 1.5(e) 0.5 24. Cirrhopet alum boninense ~5 ~I 25. Thelypteris boninensis L ~}~~ ~~~ __ ,------1 26. Seutel/aria longituba 1L 1.4 6.8 .J1 ,--- -1 27. Calanthe hattorii 1.0 28. Ma chaerina rubiginosa 0.8 0.4 29. Lindsaea repanda 0.3 1.1 30. Selaginella tamariscina 0.5 31. Sciaphila boninensis 0.01 32. Orobanche boninsimae 0.2 33. Vittar ia elongata 0.2(e) 34. Nephrolepis hirsutula 0.02 35. Sphenomeris chinensis 3.1 ,------1 36. Sehizaea boninensis I 3.4 16.5 4.7 I 5.6 37. Stachytarph etajamaicensis L~~ ~~ ~2 __J ------, 38. Fimbristylis dichotoma 4.0 17.2 39. Oxalis corniculata 0.3 2.5 40. Selaginel/a boninensis 0.5 5.0 41. Rhynchospora rubra 2.5 0.6 42. Machaerina glomerata 12.0 6.3 43. Pasparum orbiculate 4.5 4.4 44. Eleusine indica 0.5 3.1 45. Cymbopogon tortilis 0.3 6.0 46. Psilotum nudum 2.0 0.3(e) 1.1 47. Ageratum conyzoides L 0.3 2.3 -J Forest Structure on a Pacific Island-SHIMIZU AND TABATA 39

TABLE 3 (continued)

Elaeocarpus Rhaph iolepis Distylium Distylium Pinus Ardisia Li vistonia Schima Pouteria Schima SPECIES MESICFOREST DRY FOREST DRY FOREST DRY SCRUB MESIC FOREST r- ---' 48. M iscanthus condensatus v. boninensis 3.4 3.5 49. Lysimachia mauritiana 0.3 50. Digitaria platycarpha 0.6 51. Vernonia cinerea 1.6 52. Euphorb ia hirta 0.9 53. Dacty/o ctenium aegiptium 0.9 54. Sedum boninense 0.9 55. Lantana camara 0.9 56. Kalanchoe pinnata I 0.3 57. Paspalum dilatatum I 0.3

58. Youngia japon ica Li 0.3 ---l 59. Blechnum orientale 0.3 60. Cyperus cyperinus 0.04 61. Clematis terniflora 2.6(v) 62. Derris elliptica 0.7(v)

NOTE: Occurrences as epiphytes, parasites, and vines or climbers are indicated as (e), (p), and (v),respectively. Species with similar distribut ion patterns are enclosed with dashed lines.

TABLE 4 SUMMARY OFSOME CHARACTERISTICS OF FORESTS AND SCRUBON CHICHIJIMA ISLAND

Elaeoca rpus- Rhaphiolepis- Distylium- Distylium- Pinus- Ardisia Li vistonia Schima Pouteria Schima VEGETATION TYPE MESICFOREST DRYFOREST DRYFOREST DRYSCRUB MESICFOREST

No . of plots surveyed 7 10 10 10 13 Mean species no. per plot (Total species no. in all plots) Trees and shrubs 17.3 (35) 15.7 (37) 22.4 (51) 15.8 (28) 17.1 (43) Herbs and vines 6.4 (24) 6.6 (14) 11.6 (42) 12.5 (35) 8.3 (28) Mean crown height (m) (Height of Pinus lutchuensis) 12.8 5.5 6.1 1.3 9.3 (14.9) Mean no. of individuals 7,861 13,934 10,592 27,434 6,378 (E-S layers, ha- I ) Mean no. of stems 13,863 21,951 15,710 57,453 9,864 (E-S layers, ha- I) Stem no. per individual 1.76 1.58 1.48 2.09 1.55 Basal area (m2 ha - I) 6.04 3.69 4.78 1.75 5.37 Diversity index (Fisher's a) 4.1 4.3 6.6 4.1 4.8

brum , Evodia nishimurae, and flex matanoana undergrowth species such as Boninia glabra , is unique to the Distylium-Schima dry forest Callicarpa glabra , Eurya boninensis, Sympolo (Table 1), though they sometimes appear in cos pergracilis, Stachyurus praecox v. matsuza the secondary forests formed near this type of kii, Pittosporum chichisimense, and Viburnum forest. japonicum v. boninsimense, most ofwhich are The understory of this dry forest mainly peculiar to the Distylium-Schima dry forest consists ofjuveniles ofcanopy species (Figure (Table I) and are designated as endangered 5D), but it is also represented by several species (Ono et al. 1986). 40 PACIFIC SCIENCE, Volume 45, January 1991

The H layer ofthis forest contains not only highest and tot al basal area smallest ofall the many seedlings ofwoody species (Figure 5D), vegetati on types. but also a rich flora of herbaceous species Relative light intensity in the dry scru b is including Calanthe hattorii, Scutellaria longi rather high (Table 2) because of small out tuba, and Schizaea boninensis, which are also crops of lava tha t result in a par tially open found mainly in the Distylium-Schima dry canopy of stunted shrubs. Seedlings ofcanopy forest (Table 3). species are not so numerous as in the A high relative light intensity in this forest Distylium-Schima forest (Figure 5D, E ), per (Table 2), attributable to the man y small haps becau se of the arid habitat. Several canopy gaps , enables both shrub species and weedy herbs, most of which are alien species seedlings of shade-intolerant trees, like in the Bonins, are found in the canopy gaps, Schima mertensiana and Pinus lutchuensis, to and the number ofherbaceous species is com grow in the forest (Table I). The Distylium paratively large (Table 3). Schima dry forest is, therefore, characterized The scrub was severely damaged in places by the highest number of species and highest with shallow soil (that is, around lava out diversity index of all the vegetation types crops) during an unusually long drought in (Table 4). 1980. Many individuals of Distylium lepido tum died in the drought, and many new Distylium-Pouteria DRY SCRUB. Canopy canopy gaps were produced (Shimizu 1982). height decreases from Distylium-Schima dry Because there is no pioneer species such as forest to Distylium-Pouteria dry scrub with Schima mertensiana, Fagara boninensis, or out change in the dominant or subdominant Trema orientalis, which occur in mesic or dry canopy species (Table 1). Th e lowest height is forests, all stages of succession are occupied only 0.3 m (field observation). Distylium by the same members of the Distylium lepidotum is the dominan t species here, too, Pouteria scrub. and Pouteria obovata, Syzygium buxifolium, Pandanus boninensis, Ligustrum micrantum, Distribution and Rhaphiolepis indica v. integerrima are common subdominant species in both the dry Figure 7 shows a vegetation map ofChichi forest and the dry scrub (Table I). jima and Figure 8 a schematic transect profile Many species of the Distylium-Schima dry through the center of the island. Elaeocarpus forest, for example, Schima mertensiana, Ardisia mesic forest occurs in rather mesic Elaecoarpus photiniaefolius, I1ex matanoana, habitats with deep soils (Figure 8). It occupies Myrsine maximowiczii, and Machi/us boninen only 0.9% ofChichijima (Figure 7) and is now sis, cease to exist at the ecotone between the confined to a slope ofMt. Mikazuki and other dry forest and the dry scrub because of the small inland areas composed of volcanic arid condition imposed by the shallow soil breccia. The limited distribution of the forest (Table I). Two shrubs, Juniperus taxifolia and habitat was caused by its selective cutting for Dodonaea viscosa, which thrive in dry scrub, crop cultivation until 1945. Copperplate draw begin to appear at the ecotone. Several rare ings by Kittlitz (1844) and some statements and endangered shrubs such as Pittosporum in old documents (Ogasawara-Tocho 1914, parvifolium, Callicarpa nishimurae, Symplocos Fukuda 1920) suggest that dense forests kawakamii, and Myrsine okabeana are also occupied much ofChichijima before the 1830s, found in the dry scrub (Table I). The total when human s first settled the Bonins. number ofwoody species in this scrub is about Pinus-Schima mesic forest covers 36.9% of half that in the neighboring Distylium-Schima the island an d occupies almost all flat land dry forest (Table 4). and gentle slopes with fairl y deep soil of vol Almost all species have features that indi canic breccia (Figures 7,8). These places were cate drought resistance: stunted growth forms once used as cultivated fields but were with two or more stems per indi vidual (Figure abandoned after World War II (Katahira 3E) and sma ll, thick, and sometimes hairy 1981). leaves (Figure 6). Density of individuals is Species composition of the Pinus-Schima

m> ,i. ,g.; I " i ' 4 "4M . :m III E-Am.f.

Ii:9~ P-Sm.f. II R-Ld.f. mI o-ser. • D-Pd.s. Ij Rock

FIGURE 7. Vegetation map ofChichijima Island. Blank space deno tes village area, cultivated fields, coastal forests, and secondary vegetation such as Leucaena leucocephala scrub and Stachytarphetajamaicensis grassland. 42 PACIFIC SCIENCE, Volume 45, January 1991

D-Pd.s. (}OS d.f. E 300- -ClI wind E-AmJ. ¢::::::::::J -g 200- ( P-Sm.f.) « 100-

o .c- 0.:::' -ClIO OUI

FIGURE 8. Diagrammatic representation of an east-west transection through the center of Chichijima Island, showing depth of soils, kinds of basal rocks, direction of prevailing wind, and vegetation types. mesic forest is different from that of the Distylium-Schima dry forest are scattered on Elaeocarpus-Ardisia mesic forest (Figure 4), mountain tops and ridges above 150 mover probably because the area of Pinus-Schima the rest of the island and are surrounded mesic forest was once cultivated, so that hab below by Rhaphiolepis-Livistonia dry forest itat conditions shifted toward dryness (Figure 7). These small patches are thought to conditions in which the Raphiolepis-Livisonia be remnants of the former Distylium-Schima dry forest and Distylium-Schima dry forest dry forest, which once covered these areas are now supported. Most of the area now more widely than they do now (Shimizu, in occupied by Pinus-Schima mesic forest was preparation). once covered by the dense Elaeocarpus Distylium-Pouteria dry scrub, now occupy Ardisia mesic forest. ing 0.7% of the island, occurs on mountain Rhaphiolepis-Livistonia dry forest, now ridges and edges of sea cliffsofboninite pillow occupying 26.4% of the island area, is distri lava above 150 m, where thin soil with occa buted widely throughout the island (Figure 7). sional lava outcrops and the prevailing wind It covers rocky ridges on boninite pillow lava, produce arid conditions (Figures 7, 8). steep slopes with thin gravelly soils, and is Distylium-Pouteria dry scrub , with a wide found along valleys or sea cliffsirrespective of ecotonal zone (Figure 8), is usually contin basal rocks (Figure 8). Habitat conditions in uous with Distylium-Schima dry forest. this forest appear to be unstable compared with those of Distylium-Schima dry forest. Speciation Distylium-Schima dry forest, which now occupies 7.6% of the total area of the island, Representatives of some genera that seem occurs on rather flat places with thin soils of to have speciated in the Bonins were arranged boninite pillow lava. It is found mainly at in three groups based on differences in their altitudes above 150m in the northeastern part habitats: (1) those occurring in mesic and dry ofthe island (Figure 7). The most typical for forests or forest margins, (2) those composing est is found on the flat area called Chuosan the understory of Distylium-Schima dry for higashi-daira, located at the east side of Mt. est, and (3) those composing the canopy of Chuo (Figure 1). This flat is thought to be Distylium-Pouteria dry scrub (Table 5). one of the oldest landforms on Chichijima Four species of Pittosporum represent the (Tamura and Imaizumi 1981), and the habitat most prominent example of speciation in the is apparently quite stable. Small patches of Bonins (Figure 9). P. boninense is a small Forest Structure on a Pacific I sl and-SHIMIZU AND TABATA 43

TABLE 5

SI MILARITY T REND OF SPECIATION IN SIX G ENERA ON CHICHUIMA ISLAND

HABITATS OF CONGENERIC SPECIES

MESIC AND DRY FOREST UNDERSTORY OF CANOPY OF GENUS OR FOREST MARGIN D-S d.f. D-P d .s .

Bonina B. grisea B. glabra B. glabra Cal/icarpa C. subpubescens C. glabra C. nishimurae !lex I. mertensii I. percoriacea Myrsine M . maximowiczii M . okabeana Pittosporum P. boninense P. chichisimense P. parvifolium Symplocos S. pergracilis S. kawakamii

tree (1-6 m high) producing relatively large ing to P. boninense, and Callicarpa lacks one amounts of fruit dispersed by birds. It occurs comparable to P. beechyi. in a wide range of habitats on the island, but especially in sunny margins of mesic and dry forests. P. boninense is morphologically plastic compared with its congeners. It varies widely DISCUSSION in growth form and leaf size in response to Ecological Release habitat conditions. P. chichisimense and P. parvifolium, both endemic to Chichijima, are It has been suggested that the biota of rare species with distributions restricted to oceanic islands extends its habit and habitat small areas of the island. P. chichisimense is range to the extremes of physical and mor found in the understory of Distylium-Schima phological ability because competitive pres dry forest as a shade-tolerant shrub (1-2 m sure in the species-poor flora and fauna of an high); P. parvifolium grows in the canopy of island is less than on the adjacent mainland Distylium-Pouteria dry scrub, where it as (Carlquist 1974). This phenomenon is known sumes a stunted growth form (0.3-1.5 m among zoologists as ecological release (Grant high). Individuals of these two species, which 1966, Williams 1969). Diamond (1970) produce only one fruit per inflorescence, are showed that birds living on a mainland were sparsely distributed now that fertile seeds are often confined to narrow areas, while on rare. neighboring islands they occurred more P. beechyi is absent from Chichijima and widely, and explained the distribution in confined to a small area on Hahajima. It terms of release from competition. Similar occurs in dry forest and scrub comp arable to examples are known in other island birds the Distylium-Schima dry forest and Distylium (Keast 1970, Lack 1976) and in lizards Pouteria dry scrub of Chichijima, varying in (Schoener 1975, Lister 1976). growth form from stunted shrubs (0.5 m high) Some phenomena in plants may also repre to low-stature trees (3 m high). Taxonomic sent "ecological release." M etrosideros collina feature s of this species are intermediate subsp. polymorpha in Hawaii has long been between those of P. chichisimense and P. known to show a wide range of adaptations, par vifolium. spanning edaphic conditions from new lava to Similar trends in congeneric distribution mature soils, and representing some of the were observed in several other genera (Table tallest island trees in wet forests, miniature 5). Symplocos and Callicarpa especially show shrubs in bogs, and short, scrubby trees on extreme convergence with Pittosporum in ex windy ridges (Carlquist 1974). Croton scouleri ternal appearance, habit, and ecology, al in the Galapagos Islands is another example though Symplocos lacks a species correspond- that is widely distributed from arid to moist FIGURE 9. Four species of the genus Pittosporum, the most diversified woody species in the Bonin Islands. A, P. boninense; B, P. chichisimense; C, P. parvifolium; D, P. beechyi. Forest Structure on a Pacific Island-SHIMIZU AND TABATA 45 habitats and is extremely variable in leaf size and saplings can survive in the forests more (Hamann 1979a). frequently than those of other pioneer trees On Chichijima nine species, Pouteria obo such as Fagara boninensis and Trema orien vata, Hibiscus glaber, Syzygium buxifolium, talis. Once it establishes itself, it is able to Rhaphiolepis indica v. integerrima, Pandanus exist for a long time because of its coppicing boninensis, Cinnamomum insularimontanum, ability. Shimizu (1987) suggested that Pinus Ligustrum micrantum, Osman thus insularis, Schima mesicforest would change into Schima and Ficus boninensis, occur in all vegetation mertensiana forest after the nematode-caused types (i.e., the mesic forests composed of tall death of pine trees and that most individuals trees, the dry forest with low-stature trees, and of Schima mertensiana would continue to the dry scrub with stunted shrubs). Pouteria exist as dominant trees until reaching natural obovata and Hibiscus glaber, especially, senescence. change their growth forms in the different The phenomenon of a light-demanding types of vegetation. They are intrinsically species assuming a pioneer role as well as large trees more than 15 m in height and that ofa climax function seems to be another nearly 1 m in girth in Elaeocarpus-Ardisia ofthe characteristics ofoceanic island vegeta mesic forest, but individuals of the same tion. Scalesia pedunculata, a light-demanding species are stunted shrubs only 0.3 m high in tree in the Galapagos, forms a climax Scalesia Distylium-Pouteria dry scrub. forest (Hamann 1979b, Eliasson 1984, Itow Most of the nine species make a group of and Mueller-Dombois 1988). Two light subdominant species with a mix of other demanding pioneer trees, M etrosideros collina species (i.e., Elaeocarpus photiniaefolius and subsp. polymorpha and Acacia koa v. ha Ardisia sieboldii in Elaeocarpus-Ardisia mesic waiiensis, assume the role of a climax tree in forest, Pinus lutchuensis and Schima merten Hawaii's rainforests (Mueller-Dombois and siana in Pinus-Schima mesic forest, Livistonia Howarth 1981). After analyzing the death of chinensis v. boninensis in Rhaphiolepis 'ohi'a trees (Metrosideros polymorpha) in the Livistonia dry forest, Distylium lepidotum and Hawaiian Islands (the 'ohi'a dieback phe Schima mertensiana in Distylium-Schima dry nomenon), Mueller-Dombois (1983, 1986) forest, Distylium lepidotum in Distylium proposed the "cohort senescence theory," Pouteria dry scrub). Egler (1947) described which includes the phenomenon of "replace dwarf scrub on the dry ridges of Oahu in the ment dieback" in which 'ohi'a trees grow up Hawaiian Islands as ofnearly the same species in gaps under dieback canopy. Subsequently composition as that of the forests on the the 'ohi'a saplings form a new cohort stand. neighboring slope, and Mueller-Dombois These later begin to die synchronously as a (1981) showed that 33% of native plants re result of an environmental trigger when the corded along a transect on the island of Ha cohort stands reach a senescing life stage. waii were wide-ranging species that occurred from montane rainforest to subalpine condi Speciation tions. That not only a single tree but a group of dominant species occurs throughout an Adaptive radiation is one of the fascinating environmental gradient may be a phenom themes in island ecology. Prominent examples enon unique to oceanic islands. are the lobelioids of the Hawaiian Islands Schima mertensiana is one of the endemic (Rock 1919, Carlquist 1970) and Scalesia in pioneer species in the Bonins (Shimizu and the Galapagos Islands (Carlquist 1965, Tabata 1985). It also occurs in the climax Wiggins and Porter 1971, Eliasson 1984, forest (Elaeocarpus-Ardisia mesic forest, Porter 1979). Although considerable atten Raphiolepis-Livistonia dry forest, Distylium tion has been paid to adaptive radiation, Schima dry forest) as well as in secondary comparatively little is known of relationships forest (Pinus-Schima mesic forest) as a dom between speciation and the characteristics of inant species. Schima mertensiana is actually island vegetation in which speciation has a light-demanding species, but its seedlings occurred. 46 PACIFIC SCIENCE, Volume 45, January 1991

The Bonins lack many taxonomic groups be unstable compared with those of the compared with the Ryukyu Islands , the con Distylium-Schima dry forset. Because the tinental islands located nearly in the same Rhaphiolepis-Livistonia dry forest is seemingly latitude as the Bonins (see Figure 1).The flora more tolerant to typhoon attacks than the of the Bonins is especially poor in under Distylium-Schima dry forest , the canopy of growth shrub species (Shimizu 1984a). Thus this forest is not so damaged as in the the shrub layer of the forests of Chichijima is Distylium-Schima dry forest. usually composed on juveniles ofcanopy tree The Elaeocarpus-Ardisia mesic forest is a species. The only exception is in the Distylium very dark forest because of the development Schima dry forest, where several shrub species of several layers. This forest type regenerates including Callicarpa glabra, Pittosporum as a result of large-scale disturbances accom chichisimense, and Symplocos pergracilis panying many tree falls resulting from occa occur under the canopy. The canopy in the sional typhoons. Once the canopy is opened, Distylium-Schima dry forest is not fully thousands ofseedlings ofFagara boninensis or closed, perhaps because crowns of canopy Sambucus javanica germinate at once and trees have been damaged repeatedly by cover the forest floor completely for the first typhoons that occur every several decades. two years (Shimizu, in preparation). It is dif Thus , a number of seedlings and samplings ficult for some species to invade Elaeocarpus not only of shade-tolerant but also of light Ardisia mesic forest before it breaks down. demanding species like Schima mertensiana These unfavorable situations for invasion can grow together in the forest. Even an in may have prevented new species from estab troduced pioneer tree, Pinus lutchuensis, lishing in the Elaeocarpus-Ardisia mesic and invaded the forest naturally (Shimizu and the Rhaphiolepis-Livistonia dry forests. Tabata 1985). Because the habitat of Distylium-Pouteria After an exceptionally large typhoon in dry scrub is very dry, many species occurring 1983, we observed that the crowns of many in the mesic and dry forests are absent from canopy trees were blown off and that many the dry scrub; only a few species are associated small canopy gaps had formed , although with this scrub. The number of component complete tree falls were seldom found in the woody species is less than half that of the plot area (unpublished data). Because large neighboring Distylium-Schima dry forest. scale damage by typhoons had not been ob Outcrops of lava in the Dystylium-Pouteria served in this type of forest, Shimizu (1984c) dry scrub create canopy gaps ofvarious sizes. concluded that a series oftree-by-tree replace Callicarpa nishimurae, Symplocos kawakamii, ments in conjunction with small gap for and Pittosporum parvifolium, which are all mation by a single dead tree is the usual rare and now endangered, seem to be distri mechanism of regeneration. Speciation in the buted mainly on the periphery ofthese canopy Distylium-Schima dry forest thus seems asso gaps. They all have drought-resistance fea ciated with stable habitat conditions on a flat tures such as small, thick, or hairy leaves. of ancient origin, mechanisms that permit Pinus lutchuensis has also invaded Distylium moderate regeneration and canopy opening Pouteria dry scrub , especially in the canopy by occasional typhoons. gaps caused by exposed lava (Shimizu 1983). In contrast, there are no endemic under Many individuals ofthe Distylium-Pouteria growth shrubs in the Ela eocarpus-Ardisia dry scrub died as the result of an unusually mesic forest or the Rhaphiolepis-Livistonia dry serious drought in 1980(Shimizu 1982). Occa forest on Chichijima. Juveniles of canopy sional severe droughts probably occur only trees are not abundant in these forests. The once every several decades, when canopy gaps same regeneration mechanism as in the are enlarged and the chances for new species Distylium-Schima dry forest may also operate to become established in the dry scrub result. in the Rhaphiolepis-Livistonia dry forest. But Speciation seems to have occurred in those the habitat conditions of the Rhaphiolepis communities in which particular conditions Livistonia dry forest, which grows on rocky favoring formation ofnew species persist (i.e., ridges and steep gravelly slopes, seem to a comparatively small number of original Forest Structure on a Pacific Island-i-Smsnzu AND TABATA 47 component species; historically stable .hab CARLQUIST, S. 1965. Island life. The Natural itats; means of regeneration without large History Press, New York. scale disturbance; and occasional, small can - - - . 1970. Hawaii-A natural history. opy gaps). The origin of the genera shown in The Natural History Press, New York. Table 5 and the relationships among the con - - - . 1974. Island biology. Columbia Uni geners have been studied (Kanai 1977, Ono versity Press, New York. 1980, Kobayashi 1982, Kawakubo 1987, Na DIAMOND, J. M. 1970. Ecological conse gamasu 1987), but the ancestral species and quences ofisland colonization by southwest the process of speciation remain uncertain. Pacific birds, 1. Types of niche shifts. Proc. It seems that only species with high colo Natl. Acad. Sci. U.S.A. 67: 529-536. nizing ability were able to become success EGLER, F . E. 1947. Arid southeast Oahu fully established in the early island habitats. vegetation, Hawaii. Ecol. Monogr. 17:384 Among the congeners, the species found along 435. forest margins seem to show ecological be ELIASSON, U. 1984. Native climax forests. havior similar to that oftheir ancestors. Thus Pages 101-114 in R. Perry, ed. Galapagos. some populations ofthe ancestral species with Pergamon Press, Oxford. habits and habitats similar to those of the FOSBERG, F. R. 1961. Guide to Excursion III, present species occurring along the forest mar Tenth Pacific Science Congress and Uni gins shifted to the understory of Distylium versity of Hawaii, Honolulu. Schima dry forest and the Distylium-Pouteria FUKUDA, S. 1920. Ogasawara-A paradise in dry scrub, respectively, and speciated as they the Orient (in Japanese). Tokyo Engei, adapted to the new environments. Parallel Tokyo. trends in speciation in several genera support GRANT, P. R. 1966. Ecological compatibility this assumption. of bird species. Am . Nat. 100: 451-462. HAMANN, O. 1979a. On climate conditions, vegetation types, and leaf size in the Galapagos Islands. Biotropica 11: 101 ACKNOWLEDGMENTS 122. - --. 1979b. Dynamics of a stand of We are grateful to Honorary Professor H . Scalesia pedunculata Hooker fil., Santa Kazaki, Professor M. Ono, and the Ogasawara Cruz Island, Galapagos. Bot. J. Linn. Soc. Research Committee of Tokyo Metropolitan 78: 67-84. University for the use of the Chichijima Lab - - - . 1984. Changes and threats to the oratory, and to the Environmental Agency, vegetation. Pages 115-131 in R. Perry, ed. Ogasawara Branch of Tokyo Metropolitan Galapagos. Pergamon Press , Oxford. Government, the Fruit Fly Research Labo HOSOKAWA, T. 1934. Phytogeographical rela ratory of'Ogasawara Subtropical Agricultural tionship between the Bonin and the Mariana Experimental Station, and the villagers of Islands, laying stress upon the distributions Chichijima for their kind help in the study. We ofthe families, genera and the special species also thank the members ofthe Laboratory for oftheir vascular plants. J. Soc. Trop. Agric. Plant Ecological Studies, Kyoto University, 6 :201-209,657-670. for valuable discussion, and G. Murata ofthe ITOW, S., and D. MUELLER-DoMBOIS. 1988. Department ofBotany, Kyoto University, for Population structure, stand-level dieback his kind help in plant identification. and recovery ofScalesia pedunculata forest in the Galapagos Islands. Ecol. Res. 3 :333 339. LITERATURE CITED KANAI, H. 1977. On the identification char acters ofthe genus Pittosporum in the Bonin BRAY, J. R., and J. T. CURTIS. 1957. An Islands (in Japanese). Mem. Natl. Sci. Mus. ordination of upland forest communities (Tokyo) 10:59-62. of southern Wisconsin. Ecol. Monogr. KATAHIRA, H. 1981. Characteristics of the 27: 325-349. land use in Chichijima Island before World 48 PACIFIC SCIENCE, Volume 45, January 1991

War II (in Japanese). Pages 155-162 in 1981. Niche and life-form integration in Report on the assessment of the nature island communities. Pages 337-364 in of Ogasawara (2). Tokyo Metropolitan D. Mueller-Dombois, K. W. Bridges , and Government, Tokyo. H. L. Carson, eds. Island ecosystems KAWAKUBO, N. 1987. Morphological varia Biological organization in selected Ha tion of three endemic species of Callicarpa waiian communities. Hutchinson Ross (Verbenaceae) in the Bonin Islands. Plant Publishing Company, Stroudsburg, Species BioI. 1:59-68. Pennsylvania. KEAST, A. 1970. Adaptive evolution and shifts NAGAMASU, H. 1987. Notes on Symplocos in niche occupation in island birds. Biotro lucida and related species in Japan. Acta pica 2:61 -75. Phytotaxon. Geobot. 38: 283-291. KITTLITZ, F. H. VON. 1844. Vierundzwanzig NAKAMURA, T. 1985. Island of Ponape- The Vegetations-Ansichten von Kustenlan nature and the plants (in Japanese). Dai dern und Inseln des Stillen Oceans: Auf ichi-Hoki Shuppan, Tokyo. genommen in den Jahren 1827, 1828 and NUMATA, M. , and M. OHSAWA. 1970. Vegeta 1829 auf der Eutdeckungsreise der tion and succession in Chichijima, Bonin Kaiserlich-Russischen Corvette Senjawin Islands. Pages 159-197 in The nature ofthe unter Capitain Lutke. Siegen. Bonin and the Volcano Islands. Ministry of KOBAYASHI, S. 1978. A list of the vascular Education and Agency for Cultural Affairs , plants occurring in the Ogasawara (Bonin) Tokyo. Islands. Ogasawara Res. I & 2: 1-33. OGASAWARA-TOCHO. 1914. Outlines of the - - - . 1982. A taxonomical note on Pitto forests in the Bonin Islands (in Japanese). sporum tobila and its allied species. Jpn. J. Ogasawara-Tocho, Tokyo. Bot. 57:6-16. OHBA, T., and H. SUGAWARA. 1977. Vegeta KURODA, T., K . SHIRAKI, and H. URANO. tion of Chichijima and Hahajima (in 1981. Geology of the Bonin Islands (in Japanese). Pages 3-68 in Report on the Japanese). Pages 111-131 in Report on the assessment ofnew road construction at Ha assessment of the nature of Ogasawara (2). hajima in Ogasawara. Institute ofNational Tokyo Metropolitan Government, Tokyo. Parks, Tokyo. LAcK, D. 1976. Island biology, illustrated by OHGA, H. , M. KAJI, and T. NOSE. 1977. the land birds of Jamaica. University of Vegetation of Hahajima and its succession California Press, Berkeley. (in Japanese). Pages 69-101 in Report on LISTER, B. C. 1976. The nature of niche ex the assessment of new road construction at pansion in West Indian Anolis lizards, I. Hahajima in Ogasawara. Institute of Na Ecological consequences of reduced com tional Parks, Tokyo. petition. Evolution 30: 659-676. OKUTOMI, K., T . ISEK, Y. HIOKI, K. MUELLER-DoMBOIS, D. 1981. Spatial investi KITAYAMA, and H. SUMIHIRO. 1985. Vegeta gation of the organisms studied along the tion of the Ogasawara Islands (in Japa transect. Pages 181 - 210 in D. M ueller nese). Pages 97-268 in M. Ono and K. Dombois, K. W. Bridges , and H. L. Car Okutomi, eds. Endemic species and vegeta son , eds. Island ecosystems-Biological tion of the Bonin Islands. Aboc-sha, organization in selected Hawaiian com Kamakura. munities. Hutchinson Ross Publishing ONO, M. 1980. Comparison of peroxidase Company, Stroudsburg, Pennsylvania. zymograph in the Pittosporum species - --. 1983. Canopy dieback and succes endemic to the Bonin Islands (in Japanese). sional processes in Pacific forests. Pac. Sci. Proc. Jpn. Sco. Plant Taxonomists 4: 11 37:317-325. 12. - - -. 1986. Perspectives for an etiology of ONO, M., S. KOBAYASHI, and N. KAWAKUBO. stand-level dieback. Annu. Rev. EcoI. Syst. 1986. Present situation ofendangered plant 17:221 -243. species in the Bonin (Ogasawara) Islands. MUELLER-DoMBOIS, D., and F. G. HOWARTH. Ogasawara Res. 12: 1-32. Forest Structure on a Pacific Island-SHIMIZU AND TABATA 49

PORTER, D. M. 1979. Endemism and evolu - - - . 1987. Changes in species composition tion in Galapagos Islands vascular plants. and structure of Pinus lutchuensis-Schima Pages 225-256 in D. Bramwell, ed. Plants mertensiana forest after the pine wood and Islands. Academic Press, London. nematode infection at Chichijima in the RAUNKIAER, C. 1934. The life forms of plants Bonin (Ogasawara) Islands with special ref and statistical plant geography. The Cla erence to forest floor vegetation (in Japa rendon Press. Oxford. nese). Komazawa Geogr. 23 :33-60. ROCK, J. F. 1913. The indigenous trees of the SHIMIZU, Y, and H. TABATA. 1985. Invasion Hawaiian Islands. Privately published, of Pinus lutchuensis and its influence on the Honolulu. Reprinted 1974, Charles E. native fore st on a Pacific Island. J. Tuttle Co ., Tokyo. Biogeogr.12:195-207. - -- . 1919. A monographic study of the TAMURA, T., and T. IMAIZUMI. 1981.Terrestrial Hawaiian species ofthe tribe Lobelioideae, geography (in Japanese). Pages 70-84 in family Campanulaceae. Mem. B.P. Bishop Report on the assessment of the nature of Mus. 7: 1-394. Ogasawara (2). Tokyo Metropolitan Gov SCHOENER, T. W. 1975. Presence and absence ernment, Tokyo. of habitat shift in some widespread lizard TOYODA, T. 1975. Vegetation of Ogasawara species. Ecol. Monogr. 45: 233-258. National Forest with reference to Scientific SHIMIZU, Y. 1982. Influence of the drought in Reference Protection Forest (in Japanese). 1980 on the vegetation of Chichijima (in Tokyo Regional Forest Office, Tokyo. Japanese). Pages 31-37 in Report on the - --. 1981. A story ofMorus boninensis (in assessment of the nature ofOgasawara (3). Japanese). Pages 328-329 in T. Toyoda, Tokyo Metropolitan Government, Tokyo. ed. Flora of Bonin Islands. Aboc-sha, - - -. 1983. Plant ecological studies of the Kamakura. forests in the Bonin (Ogasawara) Islands (in TUYAMA, T. 1970. Plants of Ogasawara (in Japanese). Ph .D. diss., Kyoto University, Japanese). Pages 109-141 in T. Tuyama, Kyo to. and S. Asami, eds. Nature in the Bonin - --. 1984a. Comparison of the woody Islands. Hirokawa-shoten, Tokyo. species between the Bonin (oceanic) and the WIGGINS, 1. L., and D. M. PORTER. 1971. Ryukyu (continental) islands concerning Flora of the Galapagos Islands. Stanford the ecological release of plants in islands. University Press , Stanford. Ogasawara Res. 11: 1-25. WILLIAMS, E. E. 1969. The ecology of coloni - --. 1984b. Damages of the native forests zation as seen in the zoogeography of by Typhoon No. 17 (Nov. 6-7, 1983) in the anoline lizards on small islands. Q. Rev. Bonin Islands (in Japanese). Ogasawara BioI. 44: 345-389. Kenkyu-Nenpo 8:21-28. YAMAZAKI, T.1970. The vascular plants in the - --. 1984c. Regeneration of the subtro Bonin and the Volcano Islands (in Japa pical evergreen broad-leaved forest at Chi nese). Pages 95-124 in The nature of the chijima in the Bonin (Ogasawara) Islands Bonin and the Volcano Islands. Ministry of with reference to an environmental gradient Education and Agency for Cuiural Affairs , and canopy gaps . Jpn. J. Ecol. 34:87-100. Tokyo. - - - . 1986. Serious damage to Pinus lut ---. 1981. Floristic composition of the chuensis by the attack of the pine wood flora of the Bonin Islands (in Japanese). nematode at Chichijima in the Bonin Pages 303-308 in T. Toyoda, ed. Flora of (Ogasawara) Islands. J. Fac. Lett. Koma Bonin Islands. Aboc-sha, Kamakura. zawa. Univ . 44: 169-178.